ensure latest stable version is downloaded

[nabuskey]

Right now, the install script and the install instructions downloads the latest nightly release. This is not what we want. We want users to use the latest stable version.

Currently:

version=$(curl -Ls -o /dev/null -w %{url_effective} https://github.com/cnoe-io/idpbuilder/releases/latest)
version=${version##*/}
echo $version
v0.6.0-nightly.20240705 

With this PR:

version=$(curl -s https://api.github.com/repos/cnoe-io/idpbuilder/releases | grep tag_name | grep -o -e '"v[0-9].[0-9].[0-9]"' | head -n1 | sed 's/"//g')
echo $version
v0.5.0

[omrishiv]

LGTM, thanks!